Geological frame of the El Crestón molybdenum porphyry, central Sonora, Mexico

Abstract

El Crestón molybdenum porphyry, located southwest of the town of Opodepe in central Sonora, is an uncommon deposit within the porphyry copper belt of northwestern Mexico. This deposit is mostly hosted by a complex of Paleoproterozoic rocks characterized by the Crestón Granite, which yielded a U–Pb zircon age of 1,730 Ma. The mineralization is associated with a porphyry stock of sub-volcanic character, which was emplaced ~53 Ma ago during the cooling of one of the largest Laramide batholiths in the state of Sonora. The estimated reserves for this deposit are relatively small, in the order of 100 million tons, but molybdenum grades are high and reach up to 0.16%. The mineralization is disseminated as sulfides in stockwork zones, hydrothermal breccias, as well as in a relatively thin secondary enrichment blanket characterized by chalcosite. The primary mineralization consists of molibdenite and chalcopyrite associated with phyllic and potassic alteration zones. The actual structure of the deposit is quite complex mainly due to the effects of deformation related to the Tertiary extension, which dissected and rotated the original ore body. In the area of El Crestón, this deformation is represented by NE–SW and nearly N–S oriented faults, which are characteristic of the Basin and Range province.